Project Summary/Abstract Cancer treatment strategies capable of mediating antitumor response in a wide array of cancer types remain limited, even with the rapid development of novel immunotherapeutics such as checkpoint blockade. The overwhelming public health burden of cancer has created great demand for novel, broadly effective immunotherapeutics. Central to the success of essentially all cancer treatment strategies is the generation of tumor specific cytotoxic CD8+ T cell immunity, which requires potent antigen presentation by dendritic cells (DCs) since tumor cells do not efficiently present relevant CD8+ T cell epitopes. DCs must uptake tumor cells or tumor antigen and cross-present immunostimulatory peptides to CD8+ T cells. However, DCs exist as many subpopulations, and most perform subpar cross-presentation. CD103+ and CD8a+ DCs are known for their ability to process exogenous antigen and potently cross-present to CD8+ T cells. Because of this, strategies to enhance cross-presenting DC subsets could have therapeutic potential in the treatment of many cancer types. FMS-like tyrosine kinase 3 ligand (Flt3L) is a cytokine that expands and differentiates DC precursors to cross- presenting CD103+ and CD8a+ DCs, but therapeutic potential of Flt3L is limited because of its short half-life and global distribution in vivo. We have overcome the described issues of Flt3L by generating a genetic fusion of Albumin (Alb) to Flt3L named Albumin-Flt3L (Alb-Flt3L). Alb has a long half-life due to neonatal Fc receptor- (FcRn)-mediated transcytolic recycling, and exhibits trafficking to the lymphatic system as a ubiquitous serum protein. The novel immunotherapeutic Alb-Flt3L fusion protein exhibits increased half-life and selective accumulation in the draining lymph node compared to native Flt3L. Alb-Flt3L is able to expand cross- presenting DC populations in vivo, and consequently engenders potent antigen specific CD4+ and CD8+ T cell and B cell responses following protein immunization. In this study, the ability of Alb-Flt3L to induce antigen specific antitumor immunity through the expansion of cross-presenting DCs and subsequent tumor control will be investigated. Murine model of colon adenocarcinoma and model of HPV-associated cancer with be treated using Alb-Flt3L in combination with targeted radiation therapy to release tumor antigen and enhance cellular permeability. Subsequent antitumor CD4+ and CD8+ T cell and cross-presenting DC immune responses and tumor control will be evaluated. The mechanism by which Alb-Flt3L mediates its immunostimulatory function will also be interrogated using appropriate deficient mouse models. Successful completion of this proposal will generate valuable preclinical and mechanistic data regarding the therapeutic potential of Alb-Flt3L, a novel immunotherapeutic with potential efficacy as a universal strategy to treat many types of cancer. The proposed research will be conducted over a period of 3 years by the fellowship applicant under the sponsorship and guidance of Dr. T.-C. Wu at the Johns Hopkins University School of Medicine. The findings will be submitted as abstracts to national meetings as well as for publication prior to the end of the fellowship training period.